1. Field of the Invention
This invention relates to a data input display system, and more particularly to a data input display system for preparing and editing structural data having layout format constraint of constituent elements, such as mathematical formulae, chemical formulae, programming flow charts, project planning diagrams, Sequential Function charts, and other data of structure directed editors.
2. Description of the Prior Art
Structural data such as graphical positioned content of mathematical formulae has layout format constraints of its notations, for example, a fraction is composed of a denominator, a numerator and a straight line separating the fraction into two parts; the center of the denominator has to coincide with the center of the numerator; the length of the line must be equal with the longer part of the fraction; and so forth.
A conventional data input display system of this kind uses a character output device as display means, and designates character sizes and their positions by inserting instruction codes modifying inputted character strings to conform character positions to these constraints and displays them on a display screen. Therefore, complicated and troublesome procedures are necessary for inputting the instruction codes and modifying character strings. Since an input might possibly cause a syntactic error, overlap of characters occurs on the screen. Moreover, additional syntatic interpretation or reconstruction means makes the operations of the data input display system more complicated. Since the inputted characters are typically scanned on the screen as a whole and displayed again in order to decide the placement on the screen, the full screen is rewritten whenever one character is inputted; this can cause a problem of degradation of display quality. Since conventional systems are not equipped to distinguish a block area on the screen, it is not possible to assist a user with such operations as revising and updating data having format constraint within a block area.